How old and new is the camera lens?

In the purchase of lenses, especially second-hand lenses, the so-called new market described by merchants is meaningless, and there is no new definition of 99, 95 and 92 in the industry. Don't worry about whether his description is novel. Ask the seller the following points by chatting or promising before buying, and you will probably know whether it is cost-effective according to your needs and the price of the lens. If there are no problems, we can start.

Precautions:

How to choose a lens with the naked eye? When choosing a lens head, we should mainly choose from the following aspects:

First, the appearance:

1, whether the lens changes color;

2 accessories (such as hood, lens cover, etc.) are intact. ) You should have all the lenses.

3. Check the lens number (whether the product numbers on the lens, warranty card and factory card are consistent).

4. Check the bayonet. Whether the lens bayonet fits well and is not loose, and various functions (such as internal metering, TTL automatic flash, autofocus, etc. ) can be played normally.

5. Look at the glass. Check the optical glass in the lens for scratches, bubbles or obvious dust particles.

Comprehensive: the lens should be free of bubbles, dust and mildew, and the lens coating should be free of scars; There are many colors (red, yellow, blue, etc. ) on the surface of the lens, which means that it is multi-coated. If there is only blue light, then the lens can't be multi-coated. The aperture is fresh, the blades are not rusted, and the focusing ring is flexible and uniform; When the zoom lens is placed vertically, the push-pull ring should not slide down by itself; The lens shell is exquisite, with smooth surface and no scratches.

Second, the physical condition:

1. Focus accuracy check

When checking, place a piece of ground glass with appropriate size at the exposure window of the camera so that the ground glass faces forward and clings to the plane of the exposure window, then open the B or T door of the camera to view the lens resolution pattern or newspaper posted on the wall. Move the camera back and forth at the same time until the image formed on the ground glass is clear. Finally, measure the distance between the camera exposure window plane and the resolution pattern or newspaper with a ruler. If the measurement result is equal to the focal length value adjusted on the lens, it shows that the focusing accuracy of the lens is high; On the contrary, it is low.

When checking whether the zoom lens is distorted, zoom the lens to each focal length value and check whether each focal length value is distorted or not in turn.

2. Pay attention to check whether the four corners of the picture are blocked.

When checking, install the camera lens on the camera and narrow the aperture, you can find bright objects with uniform illumination and focus on them. From the viewfinder, you can observe whether the four corners of the picture are blocked, and the normal lens is not blocked.

When inspecting the zoom lens, adjust the focal length of the lens to various focal length values for inspection, and observe whether the four corners are slightly blocked at each focal length value.

3. Pay attention to the inspection of imaging deformation.

During inspection, the camera lens should be installed on a single-lens reflex camera or a direct camera, and whether the horizontal or vertical lines at close range are deformed can be observed through the viewfinder. If the horizontal line or vertical line of the object at the edge of the picture becomes arc, it means that there is distortion aberration in this lens. The greater the linear deformation, the more serious the distortion phenomenon.

Look at the camera in the shop window. If the square line is bent after imaging, the lens is deformed. In general, wide-angle lens has barrel distortion; The telephoto lens has occipital shadow distortion; There should be no obvious distortion in the standard lens.

When checking the focusing accuracy of an object at infinity, the focal length of the lens should be adjusted to the infinity mark to see whether the image on the frosted glass plate is the clearest; If it is clear, it means that the focusing accuracy is high; If the definition is poor, it means that the focusing accuracy of the lens is low.

4. Check the illumination uniformity of the image field.

Most of the defects of uneven illumination in the image field are on the short-focus lens. Therefore, when buying a short-focus photographic lens, it should be installed on the corresponding single-lens reflex camera. Through the viewfinder of the camera, the brightness of the center of the picture is exactly the same as that of the four corners. If the center is bright and the corners are dark, it means that the illumination of the image field is uneven, and the image taken by such a lens has a high center density and a low corner density.

5, check the recognition rate

Observing the scene from the viewfinder, when the focus is right and the edge line of the scene is very clear, the recognition rate of the lens is high; If it looks blurred, even red or blue double lines appear, then the lens dispersion is serious and the discrimination rate is poor.

6, check the stray light coefficient

It's sunny, neither smokeless nor foggy. If you use the viewfinder to observe the scenery, there is always a gray feeling, indicating that the lens is mixed and the quality is not good. If the scene seen in the viewfinder is transparent and clear, the lens quality is good.

7, check the color reproduction

The color restoration of the lens is very important for taking bright and realistic photos. To check the color reproduction, first remove the lens from the fuselage, remove the lens cover, adjust the aperture to the maximum, put a piece of white paper behind the lens, and point it at the fluorescent lamp in the store to see if the fluorescent lamp projected on the white paper after the lens is as white as before. This difference is very small, you have to observe it carefully to see it. If the color difference is large, it means that the color reproduction is poor and the quality is inferior.

To sum up, it is a relatively strict testing system. If it is a second-hand camera or lens, it is not so harsh. For the above items, the seller can promise that there is no problem and it is ok!